This invention relates to a process for recycling cured or partly cured polysulfide and/or polymercaptan polymer compositions.
One-component or multi-component compositions based on polysulfide polymers and/or polymercaptan polymers are used in civil engineering and building construction, in the aircraft or automotive industry, in shipbuilding and, on a large scale, in the manufacture of insulated glass. Both in the case of industrial application in automobile construction, in shipbuilding, in aircraft construction and in the manufacture of insulated glass, the sealants, adhesives or coating materials used accumulate as residual materials and waste in partly or completely cured form. Compositions based on polysulfide polymers and/or polymercaptans are distinguished in particular by their high resistance to light and ozone and by their resistance to numerous solvents and chemicals. For this reason, adhesives/sealants based on polysulfides or polymercaptans have long been used, for example, for the production of insulated glass (see, for example, H. Lucke, "Aliphatische Polysulfide", Heidelberg (1992), page 114).
In the case of one-component, systems, cured or partly cured residues are actually formed during production in the production plants; during processing, residues remain in the processing machines and processing containers. In the case of multi-component systems, partly or completely cured residues are formed in the material-carrying parts of processing machines, at the beginning of production or when the machines are switched off and when they are cleaned by "rinsing" and when excess quantities are removed during application to the structural components or vehicles. Non-reusable, solid elastomers hitherto disposed of as waste are also accumulating to an increasing extent at the end of the useful life of those parts in which the elastomers were used. Since polysulfides and--polymercaptans have already been in use for several decades as adhesives for the production of laminated insulated glass and as joint sealing compounds and coating materials in civil engineering and building construction, cured adhesives/sealants or coating materials which, hitherto, have had to be disposed as waste accumulate during rebuilding, renovation and dismantling.
Accordingly, there is a need for processes which enable these materials to be recycled.
DE-C-4142500 describes a process for recycling cured polysulfide and/or polymercaptan elastomers. According to this document, 0.5 to 400% by weight of cured elastomer are reacted in a liquid dimercapto or poly-mercapto compound to form liquid, paste-like mercapto-terminated pre-polymers and the prepolymers thus obtained are reused as polysulfide and/or polymercaptan sealing compounds. Although this method basically provides useful results, the stability in storage of the polysulfide component produced in this way is unsatisfactory. Thus, the formation of a thick skin of at least partly cured adhesive/sealant or coating material on the surface of the polysulfide-containing component is observed after only a relatively brief storage period, depending on the quantity of "recyclate" introduced. It is assumed that this hardening reaction is brought about by atmospheric oxygen in conjunction with the aminic constituents which have entered the polysulfide component through the recycling process.
Accordingly, there was a need to find an improved process for recycling cured polysulfide and/or polymercaptan compositions, in which the compositions containing the recycled products would not have any problems in regard to stability in storage.